Question: Name the isotope of ruthenium least abundant in nature ?
Paraphrase: Which isotope of ruthenium is rarest in nature?
SPARQL (Wikidata): select ?ent where { ?ent wdt:P31 wd:Q1374122 . ?ent wdt:P2374 ?obj . ?ent wdt:P279 wd:Q1086} ORDER BY ASC(?obj)LIMIT 5 
Answer: ruthenium-98, ruthenium-96, ruthenium-100, ruthenium-99, ruthenium-101